First Test: Milwaukee SwitchBlade Bits

The latest Selfeeds have replaceable blades

First Test Online Extra

John Myrtle's Tutorial on 3-Minute Sharpening of Self-Feeding Drill Bits

1.) To sharpen round self-feeding bits of any brand, I use a Dremel mini-grinder fitted with a fiber-reinforced cutoff wheel. Taking care to follow the existing angle of the teeth, I lightly grind the top side of each scoring tooth, leaving a smooth, shiny arc along the outer edge.

2.) Then I sharpen the front side of each tooth. Be sure to follow the original angle of the teeth; they are not perpendicular to the direction of rotation, but have an acute leading edge angled toward the outside.

3.) Sharpening the chip-removing blade comes next. Only flatten the smaller chisel-edge face on the end of the bit toward the feed spur, not the larger sloped face. This blade edge usually requires the most attention of the three cutting faces as it does most of the work and its thin edge is more susceptible to damage from nail strikes. I don't worry about getting this surface perfectly flat because that can require grinding too much of the bit away, and could make the cutting geometry less effective.

The chip-removing blade should contact the wood just after the outer scoring teeth. If the blade is ground too low, the scoring teeth have to gouge out a deeper channel and the added resistance can make the feed spur strip out of the wood before the blade lifts any chips. And if the outer teeth are ground too low, the blade will dive into the wood first and tear out rough chips that have not been "freed" by the scoring teeth. You can check the relationship of teeth to blade height by removing the feed spur and setting the bit down on a flat surface, but a bit will usually be fine if you sharpen it evenly every time.

With the SwitchBlade bits in my test, the blade sharpening step is made much easier by removing the blade insert and touching it up against a sanding belt or other flat abrasive. But ironically, the replaceable blade feature itself will cause the eventual demise of a bit because as the scoring teeth are ground down lower and lower, a new blade insert will eventually protrude beyond the teeth and cause ragged cuts as described above.

In theory anyway?it hasn't happened to any of mine yet

Remember, the key to successful freehand bit sharpening is to use a light touch; concentrate on just grazing the edge to a polished surface rather than grinding away enough material to change the tooth profile. If you touch up your bits when needed, you should never have to reshape the edges, just hone them sharp.

The extra life you get out of your self-feeding bits, and the faster performance of a truly sharp bit will save you both money and time.

And as always, remember to wear safety glasses; a sliver of an abrasive disc flying apart at 30,000 rpm can be a devastating little missle. This concern is also why I use fiber-reinforced cutoff wheels only.